Bridges of the Sandstone & Termite
Posted: Fri Nov 02, 2018 3:34 am
My GR needs lots of bridges – which is lucky because I like designing and building them.
So I thought I’d show a few of my creations. Please excuse the photo quality - the old pics are scanned - no digital cameras then.
Episode 1.
When I started building the SaTR, the first problem was to negotiate the big sandstone ledge. This is how it looked before I started: I finished up needing 4 bridges on this section.
The first was across a small gap between two of the large rocks, which I christened Mint gully for the plant that grows there. As I was in a hurry, my first bridge was a simple couple of bits of wood.
Many years later I got around to building a stone arch from Hebel lightweight concrete. It’s only about 40cm long but since it’s on a 1m radius curve I first had to cut the 60x20x20 cm block to fit into the gap, then cut the 1m radius curve, and then cut the arch out. For more info on using Hebel or Thermalite in UK, see my webpage here: http://www.members.optusnet.com.au/satr/hebel.htm
Here’s a train about to enter the ‘cave’. The parapets are cut separately from Hebel (very carefully – it’s fragile stuff when thin) and glued on using silicone.
Now the track had to turn back on itself, so I decided on a curved timber trestle, made from 25mm x 25mm hardwood tomato stakes. At the time I owned one loco – a Bachmann big hauler and had no idea what minimum radius to use for the curve. I could most easily build the bridge on a 75cm radius so, much to my future regret, that’s what I used. The Big Hauler seemed OK on this radius. (I was building my own track too.) The track is also on a 1:25 grade. I even turned the posts on my lathe to a ‘rough round’ to simulate tree trunks.
Here it is on opening day in 1994.
As that pic shows, it lead onto a steel arch bridge and then a timber truss. (I’ll return later to the replacement of the trestle on a larger radius.)
The steel arch was made from some leftover steel from an above ground swimming pool, 25x25mm steel angle and 6x3mm flat steel for the hangers. As I pop-rivetted each part I dunked the parts in ‘Kill Rust’ paint so there was a good covering at joints. There has been no rust in over 20 years.
The 1m long timber truss is made from 25mm x 25mm tomato stakes. I took the easy way out and made all angles 45 degrees. The vertical tension members are 3mm threaded steel rod so they can be tightened to the correct tension to hold the whole thing together. There’s no glue. I tested it by standing on it before installation. It’s still in service after 24 years.
After 6 years of trying to run longer trains around the 75cm radius curve, up a 1:25 grade, I decided it was time for a deviation. By building a new trestle using posts up to 1.2m long, I could get a 1m radius. I reused the arch and truss bridges but in the process I ‘transposed’ their locations.
These pics shows the before, during and after alignments.
This time I used 20mm x 20m tomato stakes so they look more slender.
The old trestle was ‘saved’ by the local Historical Society, but with no funds to maintain it, it is slowly falling apart.
This pic illustrates the new arrangement of the truss and steel arch bridges and the curved deviation cut into the rock.
This pic shows the long posts I needed to get the 1m radius. Any larger radius would have needed posts down to ground level. It also shows how very difficult it was to layout the new curve ‘in mid air’ on the 1:25 grade, with no level ground underneath for a reference.
I wanted a ‘fence’ to catch derailments but after much testing I decided I didn’t need a continuous fence but just the posts – if they were close enough together. Much testing using an old 4 wheel wagon pushed at speed to derail convinced me a separation of170 mm would not allow any vehicle to miss posts. They are just visible in the above pic.
This shows that the tree is leaning onto the truss. I have removed the bark on a couple of occasions to give clearance, but ‘soon’ I will have to replace the bridge – maybe just turn it upside down.
In the next episode, we’ll move along the line to Melaleuca and the biggest of bridges.
So I thought I’d show a few of my creations. Please excuse the photo quality - the old pics are scanned - no digital cameras then.
Episode 1.
When I started building the SaTR, the first problem was to negotiate the big sandstone ledge. This is how it looked before I started: I finished up needing 4 bridges on this section.
The first was across a small gap between two of the large rocks, which I christened Mint gully for the plant that grows there. As I was in a hurry, my first bridge was a simple couple of bits of wood.
Many years later I got around to building a stone arch from Hebel lightweight concrete. It’s only about 40cm long but since it’s on a 1m radius curve I first had to cut the 60x20x20 cm block to fit into the gap, then cut the 1m radius curve, and then cut the arch out. For more info on using Hebel or Thermalite in UK, see my webpage here: http://www.members.optusnet.com.au/satr/hebel.htm
Here’s a train about to enter the ‘cave’. The parapets are cut separately from Hebel (very carefully – it’s fragile stuff when thin) and glued on using silicone.
Now the track had to turn back on itself, so I decided on a curved timber trestle, made from 25mm x 25mm hardwood tomato stakes. At the time I owned one loco – a Bachmann big hauler and had no idea what minimum radius to use for the curve. I could most easily build the bridge on a 75cm radius so, much to my future regret, that’s what I used. The Big Hauler seemed OK on this radius. (I was building my own track too.) The track is also on a 1:25 grade. I even turned the posts on my lathe to a ‘rough round’ to simulate tree trunks.
Here it is on opening day in 1994.
As that pic shows, it lead onto a steel arch bridge and then a timber truss. (I’ll return later to the replacement of the trestle on a larger radius.)
The steel arch was made from some leftover steel from an above ground swimming pool, 25x25mm steel angle and 6x3mm flat steel for the hangers. As I pop-rivetted each part I dunked the parts in ‘Kill Rust’ paint so there was a good covering at joints. There has been no rust in over 20 years.
The 1m long timber truss is made from 25mm x 25mm tomato stakes. I took the easy way out and made all angles 45 degrees. The vertical tension members are 3mm threaded steel rod so they can be tightened to the correct tension to hold the whole thing together. There’s no glue. I tested it by standing on it before installation. It’s still in service after 24 years.
After 6 years of trying to run longer trains around the 75cm radius curve, up a 1:25 grade, I decided it was time for a deviation. By building a new trestle using posts up to 1.2m long, I could get a 1m radius. I reused the arch and truss bridges but in the process I ‘transposed’ their locations.
These pics shows the before, during and after alignments.
This time I used 20mm x 20m tomato stakes so they look more slender.
The old trestle was ‘saved’ by the local Historical Society, but with no funds to maintain it, it is slowly falling apart.
This pic illustrates the new arrangement of the truss and steel arch bridges and the curved deviation cut into the rock.
This pic shows the long posts I needed to get the 1m radius. Any larger radius would have needed posts down to ground level. It also shows how very difficult it was to layout the new curve ‘in mid air’ on the 1:25 grade, with no level ground underneath for a reference.
I wanted a ‘fence’ to catch derailments but after much testing I decided I didn’t need a continuous fence but just the posts – if they were close enough together. Much testing using an old 4 wheel wagon pushed at speed to derail convinced me a separation of170 mm would not allow any vehicle to miss posts. They are just visible in the above pic.
This shows that the tree is leaning onto the truss. I have removed the bark on a couple of occasions to give clearance, but ‘soon’ I will have to replace the bridge – maybe just turn it upside down.
In the next episode, we’ll move along the line to Melaleuca and the biggest of bridges.